Choosing the right drop cable interconnect solution is a crucial step for FTTH network deployment. It is for both ends of the drop cable—the distribution point and the home's optical network terminal (ONT) or the network interface device (NID). There are two choices: splices (permanent joint) and connectors (easily mated and unmated). These two options are both widely used at the distribution point, but at the ONT/NID, a field-terminated connector or a spliced-on factory-terminated connector would be a preferable choice. They both have their pros and cons. This post will discuss these two interconnect solutions for FTTH drop cables.

Pros: Splices can make sure excellent optical performance. Splicing can eliminate the possibility that the interconnection point becomes dirty or damaged. A dirty or damaged point may potentially compromise signal integrity, as may happen to a connector end face when it is handled while unmated. Contaminants will cause high optical loss or even permanently damage to the connector end face. And splice enables a transition from 250µm drop cable to jacketed cable.

Cons: Splice lacks operational flexibility. To reconfigure a drop cable at the distribution point, one splice must be removed, fibers rearranged, and new fibers spliced, which requires the technician to carry special splicing tools for simple subscriber changes. During this time, other customers' service may be disrupted by the fiber-handling process. 250µm fiber cable is usually used at the distribution point, which is easily bent and then causes high optical loss or even break the fiber. Besides, if a splice is used at the ONT, a tray is needed to hold and protect the splice, which increases the ONT size and potentially the cost.

Pros: Connectors can be mated and unmated repeatedly, which makes them provide greater network flexibility. For example, to connect or disconnect an SC to ST fiber cable connection, without any tools, a technician can just easily plug or pull out the SC connector and ST connector on two ends. Connectors can also provide access points for networking testing.

Cons: Material cost is connectors' the most obvious downside. They cost more than splices, although network rearrangement with connectors is much cheaper. Providers need to weigh connectors' material cost and their potential for contamination and damage against the great flexibility and low network management expense.

Splice is appropriate for drops where there is no need for future fiber rearrangement, typically in a greenfield or new construction application where all of the drop cables could be easily installed during the living unit construction. Once the decision goes to splices, the type of splicing (fusion and mechanical) must be determined.

Fusion splicing has been the de facto standard for fiber feeder and distribution construction networks. Fusion splicer is used for FTTH drop splicing as it provides a high quality splice with low insertion loss and reflection. However, the initial capital expenditures, maintenance costs and slow installation speed of fusion splicing hinder its status as the preferred solution. Fusion splicing is suitable for companies which have invested in fusion splicing equipment and have no need to purchase additional splicing machines. Mechanical splices are successfully deployed around the world in FTTH installation, but not popular in United States because the index matching gel inside the splices can yellow or dry out, resulting in service failures. Great strides have been made in improving gel performance and longevity over the last 20 years.

Connectors could be used to connect different subscribers as needed for distribution points. It must be installed at the ONT and then offers flexibility both at the curb and at the home. Once the decision goes to connectors, factory-terminated connectors or field-terminated connectors must be decided.

Factory-terminated cables, such as LC to LC cable or SC to LC cable, which means the connectors you specify are pre-terminated for you, provide high-performance and reliable connections with low optical loss. By reducing installation time, factory termination keeps labor costs low. But factory-terminated cables are expensive compared to field-terminated alternatives. And they require a cable management system to store slack cable at the curb or in home. The installation of field-terminated connectors can be customized by using a reel of cable and connectors. Fuse-on connectors use the same technology as fusion splicing to provide the highest level of optical performance in a field-terminated connector. Mechanical connectors provide alternatives to fuse-on connectors for field installation of drop cables. Depending upon service provider requirements and living unit configurations, a hybrid solution of a field-terminated connector on one end of the drop cable and a factory-terminated connector on the other may be the optimal solution.

Choosing the right drop cable interconnect solution is a key and important step for a successful FTTH network deployment. Making the right connection option will not only offer cost savings and efficient deployment but also provide reliable service for customers. Splices and connectors are two options for you. They have their advantages and disadvantages. A better understanding of them two can help you make a more suitable choice.

Posted by: jowang at 02:42 AM | No Comments | Add Comment
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